The present invention relates to a method of exposure, exposure apparatus, photomask, method of production of a photomask, microdevice, and method of production of a microdevice.
In the photolithographic process for production of a semiconductor integrated circuit, liquid crystal display element, thin film magnetic head, pickup element, or other microdevice, a pattern of a photomask is transferred to a semiconductor wafer or glass plate coated with a photoresist (hereinafter also called a xe2x80x9cphotosensitive substratexe2x80x9d). As this type of projection exposure apparatus, wide use has conventionally been made of a step-and-repeat type exposure apparatus (stepper). This step-and-repeat type exposure apparatus reduces and projects the pattern of the photomask all together on each shot area of a wafer for exposure. When finishing exposing one shot area, it moves the wafer and exposes the next shot area. This action is successively repeated.
To enlarge the scope of exposure of the mask pattern, a step-and-scan type exposure apparatus has been developed which restricts the exposure light from the illumination system to a slit shape (for example, a rectangular shape), uses this slit light to reduce and project part of the mask pattern on the wafer, and makes the mask and wafer synchronously move to be scanned by the projection optical system in that state. This step-and-scan type exposure apparatus (scanning stepper) has both the advantage of the transfer method of an aligner of transferring the pattern of the entire mask on the entire surface of the wafer by an equal magnification using a single scanning light beam and the advantage of the transfer method of the above stepper. Note that the photomask used in this step-and-repeat or step-and-scan reduction projection type exposure apparatus is also called a xe2x80x9creticlexe2x80x9d.
The photomask used in this type of exposure apparatus has conventionally been produced by using an electron beam lithography system or a laser beam lithography system to draw a master pattern on a photomask substrate. That is, a mask material has been formed on the substrate, a resist coated, then an electron beam lithography system or laser beam lithography system used to draw the master pattern. Next, the resist has been developed, then etched etc. to form the master pattern by the mask material. In this case, if the reduction magnification of the reduction projection type exposure apparatus using this photomask is 1/xcex2, the master pattern drawn on the photomask may be a xcex2-fold enlarged pattern of the device pattern, so the drawing error of the lithography system is reduced to about 1/xcex2 on the device. Therefore, it becomes possible in practice to form the device pattern by a resolution of about 1/xcex2 the resolution of the lithography system.
In a projection exposure apparatus producing a microdevice using such a photomask (hereinafter sometimes referred to as a xe2x80x9cdevice exposure apparatusxe2x80x9d), there is distortion or coma aberration or other aberration of the projection optical system, projection magnification error, drawing error of the pattern of the photomask, rotation, shift, and other offset of the photomask with respect to the projection optical system, bending and other deformation error of the photomask accompanying holding on the stage, and other error, so there was the problem that error occurred in the position or shape of the pattern formed on the substrate for producing the device and the characteristics of the microdevice produced deteriorated.
Further, in the above way, in the past, the master pattern of the photomask had been drawn by an electron beam lithography system or laser beam lithography system. These lithographic systems draw the master pattern directly based on drawing data from a control computer. Recent LSIs and other devices, however, have become larger in area and have been increasingly improved in fineness and integration, so the master pattern required for the exposure has also become larger in area and finer. Further, as the photomask, use has been also made of reticles provided with correction patterns for preventing transfer of unnecessary patterns by double exposure, so-called phase shift reticles providing a phase shift between adjoining patterns, etc., but with such special photomasks, the amount of the drawing data tends to become greater than that of other photomasks. Due to this, the drawing data required by the lithography system for producing the photomask becomes massive.
Therefore, the drawing time required for drawing the master pattern of a single photomask by the lithography system has recently grown from 10 hours to as much as 24 hours or so. This longer drawing time has become one factor behind the rising cost of production of photomasks.
In this regard, in an electron beam lithography system, it is necessary to correct for the proximity effect due to the back scattering distinctive to electron beams. Further, it is necessary to correct for electric field unevenness at the periphery of the substrate due to the charging of the surface of the substrate. Therefore, to draw the master pattern as designed, it is necessary to measure for error in the drawing position etc. in advance under various conditions and make complicated corrections at the time of drawing with a high accuracy and stability. Making such complicated corrections during the above extremely long drawing time with a high accuracy and stability, however, is difficult. The problem of drift in the drawing position occurs during the drawing. Further, it is possible to interrupt the drawing and calibrate for error, but this has the problem of further increasing the overall drawing time.
Further, the resolution and other characteristics of resists for electron beams have not been improved that much and there will probably not been any rapid improvement in these characteristics in the future either. Therefore, if the pattern rule of semiconductor devices etc. becomes further finer in the future, the drawing time for the master pattern of one photomask will become too long, the resolution of the electron beam resist will approach its limits, and the necessary drawing accuracy may no longer be obtained. Further, the amount of the drawing data in the control computer is also becoming so massive as to be difficult for use in a single drawing process.
On the other hand, a laser beam lithography system draws a master pattern using an ultraviolet band laser beam. It has the advantages that a resist offering a higher resolution than an electron beam lithography system can be used and there is no proximity effect due to back scattering. The resolution of a laser beam lithography system, however, is inferior to that of an electron beam lithography system. Further, a laser beam lithography system is also a system which draws the master pattern directly, so the amount of the drawing data becomes massive, the processing of the data is becoming difficult, and the drawing time is becoming extremely long. Therefore, the required drawing accuracy may no longer be able to be obtained due to drift etc. of drawing position etc.
Further, a working mask is sometimes produced by a projection exposure apparatus transferring the pattern formed on the master mask to a photomask substrate (blank) (hereinafter also referred to as a xe2x80x9creticle exposure apparatusxe2x80x9d), but due to analogous problems as with the above device exposure apparatus for producing a microdevice, that is, distortion and coma aberration and other aberration of the projection exposure apparatus, projection magnification error, drawing error of the pattern of the master mask (master drawing error), rotation, shift, and other offset of the master mask with respect to the projection optical system, bending and other deformation error of the master mask due to holding on the stage, and other error, error occurs in the position and shape of the pattern formed on the blank, the continuity and periodicity of the pattern become poor particularly at the stitching portions, the accuracy of the photomask produced deteriorates, and the accuracy of the microdevice produced using such a photomask deteriorates.
Further, when actually mounting the photomask in a projection exposure apparatus and projecting the pattern of the photomask on a wafer or other device substrate through a projection optical system, the image of the photomask projected on the surface of the device substrate deforms due to the bending of the photomask along with holding, tilt with respect to the reference plane (object plane of projection optical system), phase shift, etc., deforms due to distortion or field curvature or other aberration of the projection optical system, and sometimes deforms due to even bending of the device substrate etc. A pattern distorted from the ideal image (ideal pattern) ends up being transferred and formed on the device substrate. As a result, the overlay error etc. of the pattern increases and the characteristics of the microdevice produced sometimes deteriorate. Further, the imaging characteristics of the projection optical system differ slightly with each projection exposure apparatus, so it is desirable to correct the projected image for each projection exposure apparatus.
Here, for the aberration of the projection exposure system, techniques such as arranging a glass plate or aberration correcting plate in the optical path, providing a mechanism for fine movement of the lenses comprising the projection optical system, or sealing the gas chamber between lenses of the projection optical system and changing the pressure or composition of the gas there are sometimes used, but even such techniques are unable to completely eliminate the aberration. It is necessary to correct the residual aberration or improve the exposure accuracy by a simpler configuration.
Further, if using an electron beam lithography system or laser beam lithography system to produce a photomask, rotation or offset or other error sometimes occurs due to the drawing error etc. between an alignment mark of the photomask and the drawn master pattern. Therefore, even if using the alignment mark of the photomask for complete alignment with the device substrate (wafer) in transfer and exposure of the pattern, error remains between the alignment mark of the photomask and the master pattern, so there is the problem that rotation or offset occurs in the pattern transferred to the device substrate, the overlay accuracy of the pattern deteriorates, and the characteristics of the microdevice produced otherwise deteriorates in some cases.
Note the method of reducing the rotation, offset, or other error includes not only improvement of the basic accuracy of the lithography system, but also drawing the same pattern overlaid several times for averaging, but even normally the drawing time takes from several hours to tens of hours, so drawing several times increases the drawing time tremendously and therefore this is impractical. Further, sometimes the rotation, offset, and other error occurring between the master pattern and an alignment mark of the photomask is measured in advance and the position of the device substrate is corrected using the measured value at the time of exposure on to the device substrate, but the processing is complicated and the accuracy was also insufficient.
Therefore, an object of the present invention is to produce a high accuracy, high quality microdevice.
Another object of the present invention is to produce a high accuracy, high quality microdevice efficiently in a short time.
1. According to a first aspect of the present invention, there is provided a method of projecting and exposing a pattern (Pi) formed on a mask (Ri) on to a photosensitive substrate (4) through a projection optical system (3), the method of exposure characterized by measuring a position of an image projected by the projection optical system and projecting and exposing the pattern of the mask in a state with imaging characteristics corrected to reduce an amount of offset of the position of the projected image from an ideal position.
According to this method of exposure of the present invention, since the imaging characteristics are corrected so as to reduce the amount of offset of an image projected by the projection optical system from the ideal position, it is possible to reduce the error arising in the position or shape of a pattern formed on the photosensitive substrate caused by distortion or coma aberration or other aberration of the projection optical system, projection magnification error, error in the pattern formed on the mask, rotation, shift, or other positional error of the mask from the projection optical system, bending of the mask along with holding, and other deformation error and therefore possible to produce a high accuracy, high quality microdevice or photomask etc.
Note that there are various methods for correction of the imaging characteristics and the method is not particularly limited. For example, they may be corrected by providing a mechanism for fine movement of the lenses comprising the projection optical system, inserting a wedge-like glass plate or other aberration correcting plate in the optical path, sealing the gas chamber between lenses in the projection optical system and changing the pressure or composition of the gas, or tilting the mask or photosensitive substrate with respect to the object plane of the projection optical system.
2. According to a second aspect of the present invention, there is provided a method of projecting and exposing a pattern (Pi) formed on a mask (Ri) on to a photosensitive substrate (4) through a projection optical system (3), the method of exposure characterized by forming a first mark (53) on the mask; measuring a position of an image projected by the projection optical system of a second mark (64, 65, 66) of a control use reference mask (60) formed with the second mark and a third mark (63) corresponding to the first mark and defining it as a second image position; finding the position of an image projected by the projection optical system of the third mark in a state with imaging characteristics preliminarily corrected to reduce an amount of offset of the second image position from an ideal position and defining it as a third image position; measuring a position of an image projected by the projection optical system of the first mark of the mask and defining it as a first image position; and projecting and exposing the pattern of the mask in a state with imaging characteristics corrected so that the first image position becomes one of a predetermined positional relationship with the third image position.
First, the first mark is formed on a working mask for producing the microdevice or a mask serving as the master mask for producing the working mask. Further, a control use reference mask formed with the third mark at a position corresponding to the first mark (for example, a facing position) and formed with the second mark at a position not corresponding to the first mark is prepared separately from the mask.
Next, the position of the image projected by the projection optical system of the second mark of the control use reference mask (for example, the position in the plane orthogonal to the optical axis of the projection optical system) is measured. The thus measured image position of the second mark is referred to as the second image position. Next, the amount of offset of the second image position from its ideal position (ideal lattice) is found and the imaging characteristics are corrected to reduce the amount of offset, for example, by adjusting the projection magnification etc. The image position of the third mark at this time is found by measurement. The thus measured image position of the third mark is referred to as the third image position. The third image position may also be found by measuring the image position of the third mark before correction of the imaging characteristics and calculating from the measured value. Due to this, the image position of the third mark is found in a state with the imaging characteristics in the pattern area (first area) desirably corrected. This constitutes the advance preparations.
Next, the position of the image projected by the projection optical system of the first mark of the mask is measured. The thus measured image position of the first mark is referred to as the first image position. Next, the imaging characteristics are corrected so that the first image position becomes one of a predetermined positional relation with the third image position (for example, so that they are substantially in register). By correcting the imaging characteristics in this way, it is possible to reproduce imaging characteristics when using the control use reference mask to correct the image position of the second mark (mark formed in first area corresponding to pattern area) to approach the ideal position. Therefore, by transferring the pattern of the mask on to the photosensitive substrate in this state, it is possible to form a high accuracy pattern close to the ideal pattern without distortion or other error in the position or shape of the pattern.
3. According to a third aspect of the present invention, there is provided a method of exposure dividing an enlarged pattern of a pattern for transfer (27) into patterns of a plurality of masks (Ri) and projecting and exposing images reduced by a projection optical system (3) of the patterns (Pi) of a plurality of masks on a surface of a photosensitive substrate (4) while stitching them, the method of exposure characterized by forming a first mark (53) in a peripheral area (52) of a pattern area (51) of a mask in which a pattern is formed; measuring a position of an image projected by the projection optical system of a second mark (64, 65, 66) of a control use reference mask (60) formed with a plurality of the second marks in a first area (61) corresponding to the pattern area of the mask and formed with a third mark (63) facing the first mark in a second area (62) corresponding to the peripheral area of the mask and defining it as a second image position; finding a position of an image projected by the projection optical system of the third mark in a state with the imaging characteristics preliminarily corrected to reduce the amount of offset of the second image positions from their ideal positions and defining it as a third image position; measuring a position of an image projected by the projection optical system of the first mark of the mask and defining it as a first image position; and successively projecting and exposing patterns of the masks in a state with imaging characteristics corrected so that the first image position becomes in register with or proximity to the third image position.
Note that in the specification of the present application, xe2x80x9cstitchingxe2x80x9d means exposure by overlapping a processing area by one exposure with part of a processing area of another exposure and includes the case of stitching in a direction along the patterns (lines)(connecting lines) and the case of stitching in a direction intersecting the patterns (lines) (arranging lines).
According to the present invention, an enlarged pattern of the pattern for transfer is divided into patterns of plurality of masks and images reduced by the projection optical system of the patterns of the plurality of masks are successively projected and exposed on the surface of the photosensitive substrate while stitching them. When producing a photomask (working mask) for use in production of a microdevice, as one example, a thin film of the mask material is formed on the mask substrate (blank) serving as the substrate of the photomask and a photoresist or other photosensitive material is coated on top. Next, reduced images of the patterns of a plurality of master masks are transferred on to the photosensitive material using for example an optical type reduction projection exposure apparatus by step-and-repeat or the step-and-scan, then the photosensitive material is developed. Next, the pattern of the remaining photosensitive material is used as a mask for etching etc., whereby the desired pattern for transfer (master pattern) is formed.
At this time, if the reduction magnification of the optical type exposure apparatus for production of the photomask is 1/xcex1 (xcex1 is an integer, fraction, etc. greater than 1), the pattern for transfer, that is, the master pattern, is enlarged xcex1-fold. The enlarged master pattern is divided into patterns of xcex1xc3x97xcex1 number of master masks in the vertical and horizontal directions. If the reduction magnification is ⅕ (xcex1=5), 5xc3x975 or 25 master masks are prepared. As a result, the pattern formed in each master mask becomes part of a master pattern of an a-fold enlargement of the master pattern, so the amount of drawing data of the pattern of each master mask is reduced to about 1/xcex12 of the past and the minimum line width becomes a times that of the past. Therefore, the pattern of each master mask can be drawn by a high accuracy with little drift in a short time using for example a conventional electron beam lithography system or laser beam lithography system. Further, the drawing error due to the lithography systems is reduced to 1/xcex1 on the photomask, so the accuracy of the master pattern is improved more. Further, after producing the master masks, the patterns of the master masks can be transferred at a high speed on to the substrate of the photomask by a step-and-repeat etc., so the production time when producing several photomasks can be greatly reduced compared with the method of drawing individually by a lithography system as in the past.
Further, when there is a partial mistake in the formation of the pattern of a master mask or when there is a later change in part of the master pattern, it is sufficient to correct or remake only the master mask including the part with the mistake or the master mask including the changed portion. There is no effect on the plurality of master masks as a whole, so even in this case, the correction or change can be handled efficiently.
Note that above the explanation was given of the case of production of a working mask, but the same applies to the case of producing a microdevice (for example a liquid crystal display) by successively projecting and exposing patterns of a plurality of working masks on the surface of a device substrate (wafer or glass substrate) while stitching them.
Here, when successively projecting and exposing patterns while stitching them, the positional accuracy or shape accuracy at the connecting parts of the patterns transferred by the masks has a great effect on the characteristics of the microdevice etc. produced, so a high positional or shape accuracy of the patterns is also very important.
Therefore, in this method of exposure of the present invention, in the same way as the method of exposure according to the second aspect of the present invention, first the first mask is formed at the peripheral area of the working mask for producing the microdevice or master mask for producing the working mask (area outside of pattern area in which pattern to be transferred is formed). Further, the control use reference mask formed with the third mark at a position corresponding to the first mark (for example, a facing position) and formed with the second mark at an area corresponding to the pattern area is provided separate from the mask.
Next, the position of the image projected by the projection optical system of the second mark of the control use reference mask (for example, position in the plane orthogonal to the optical axis of the projection optical system) is measured. This measured image position of the second mark is referred to as the xe2x80x9csecond image positionxe2x80x9d. Next, the amount of offset of the second image position from the ideal position (ideal lattice) is found and the imaging characteristics are corrected by for example adjusting the projection magnification etc. so as to reduce the amount of offset. The image position of the third mark at this time is measured. This measured image position of the third mark is referred to as the xe2x80x9cthird image positionxe2x80x9d. This third image position may also be found by measuring the image position of the third mark before correction of the imaging characteristics and calculating from the measured value. This enables the image position of the third mark to be found in the state with the imaging characteristics in the pattern area (first area) suitably corrected. This constitute the advance preparations.
Next, the position of the image projected by the projection optical system of the first mark of the mask is measured. The thus measured image position of the first mark is referred to as the xe2x80x9cfirst image positionxe2x80x9d. The imaging characteristics are corrected so that the first image position becomes in register with or in proximity to the third image position. By correcting the imaging characteristics in this way, it is possible to reproduce imaging characteristics as with correction using the correction use reference mask so that the image position of the second mark (mark formed at first area corresponding to pattern area) approaches the ideal position. Therefore, by transferring the pattern of the mask on to the photosensitive substrate in this state, there is little distortion or other error in the position or shape of the pattern and it is possible to form a high accuracy pattern close to the ideal pattern.
4. According to a fourth aspect of the present invention, there is provided a method of projecting and exposing a pattern (Pi) formed on a mask (Ri) on to a photosensitive substrate (4) through a projection optical system (3), the method of exposure characterized by making part or all of the pattern reach a peripheral area (52) of a pattern area (51) of the mask in which a pattern is formed and defining the portion of the pattern present at the peripheral area as a mark portion (73) for measurement of a spatial image; measuring a position of an image projected by the projection optical system of the mark portion of the mask by a spatial image measurement method; and correcting imaging characteristics so as to give the smallest amount of offset of the image position of the mark portion from its ideal position and exposing and projecting the pattern of the mask in a state with the mark portion shielded by a blind.
According to this method of exposure of the present invention, since part or all of the pattern is made to reach the peripheral area, that part is used as a mark portion, the position of its projected image is measured, and the imaging characteristics are then corrected, the accuracy of the pattern near the boundary of the pattern area with the peripheral area becomes high and when projecting and exposing the patterns of a plurality of masks successively on the substrate while stitching them etc., the continuity (for example, the continuity when connecting in a direction along the lines in the case of a line-and-space (L/S) pattern) or periodicity (periodicity of array of direction orthogonal to the lines in the case of an L/S pattern) of the connection portion of a pattern formed using one mask with an adjacent other pattern formed using another mask can be made extremely good.
Further, when measuring the projected image of a mark, if the shape of the mark or the shape of the pattern (for example, thickness) differs, while depending on the measurement method, a difference sometimes occurs in the coma aberration or distortion when measuring by for example the spatial image measurement method. In the present invention, the mark portion is the same in shape as the pattern of the pattern area, so this problem does not arise. Note that the mark portion is shielded by a blind at the time of exposure, so the mark portion is not transferred on to the photosensitive substrate.
5. According to a fifth aspect of the present invention, there is provided a method of exposure dividing an enlarged pattern of a pattern for transfer (27) into patterns of a plurality of master masks (R1 to RN) and projecting and exposing images reduced by a projection optical system of the patterns of a plurality of master masks on a surface of a mask substrate while stitching them, the method of exposure characterized by finding a displacement of an actually projected point (xcex11) on the mask substrate from an ideal projected point (xcex11) and making at least part of the pattern (36) formed on the master mask distort based on the found displacement or making the position of the pattern of the master mask at the object plane side of the projection optical system shift.
The displacement found here includes displacement arising due to at least one of deformation of the pattern of the master mask (deformation due to bending of the master mask along with holding, the tilt with respect to the reference plane (object plane of projection optical system), phase shift, etc.), aberration of the projection optical system (distortion, image plane curvature, astigmatism, coma aberration, spherical aberration, etc.), and deformation of the mask substrate (bending etc.).
According to this aspect of the present invention, the displacement of an actual projected point (xcex11) on the mask substrate from the ideal projected point (xcex11) is found and the pattern (36) formed on the master mask is distorted for formation based on the found displacement. For example, a predetermined sampling point (xcex10) is set on the master mask, the displacement (offset) of the actual projected point (xcex11) corresponding to the sampling point with respect to the ideal projected point (xcex11) on the mask substrate is theoretically calculated or is found by performing actual exposure and measuring the displacement of the transferred image by a measuring device, the distortion of the image of the pattern on the mask substrate (4) is found based on this, and the original pattern to be formed on the pattern mask (pattern in design) is made to distort to substantially eliminate this distortion, that is, the data of the pattern in the design is corrected to form (draw) the pattern.
The sampling point may be made a plurality of points arranged at a suitable pitch along the design pattern or in an ideal lattice. The correction values of the data at each point in the design pattern may be found based on the displacement found by the least square method or another approximation method, for example, by preparing a correction value map and interpolating using that data. Since the original pattern (design pattern) is made to distort so that the actual projected image becomes substantially in register with the ideal projected image, even if for example there is residual aberration of the projection optical system etc., it is possible to project and transfer a pattern close to the ideal image on to the mask substrate and possible to produce a high accuracy, high quality photomask. Note that instead of causing distortion of at least part of the pattern, it is also possible to cause the pattern position at the object plane side of the projection optical system to shift or to combine the two techniques.
The photomask of the present invention produced using the above method of exposure for producing the photomask is formed with a pattern close to the ideal image, so is high in accuracy and high in quality. By using such a photomask (working mask) for exposure of a device substrate, it is possible to improve the overlay accuracy of the pattern and produce a microdevice having superior characteristics.
6. According to a sixth aspect of the present invention, there is provided a method of exposure projecting an image of a pattern of a master mask on a mask substrate (4) by a first projection optical system (3) to produce a working mask (34) and projecting and exposing an image of the pattern of the working mask on a device substrate (W) on which a microdevice is to be formed by a second projection optical system (42), the method of exposure characterized by finding at least one of a displacement of an actually projected point (xcex21) on the mask substrate from an ideal projected point (xcex11) and a displacement of an actual projected point (xcex21) on the device substrate from an ideal projected point (xcex11) and making at least part of the pattern (36) formed on the master mask distort based on the found displacement or making the position of the pattern of the master mask at the object plane side of the projection optical system shift.
In this case, it is possible to divide an enlarged pattern of a pattern for transfer (27) into patterns of a plurality of master masks (R1 to RN) and successively expose reduced images of the master patterns on a surface of the mask substrate (4) while stitching them.
The displacement found here includes displacement arising due to at least one of deformation of the pattern of the master mask (deformation due to bending of the master mask along with holding, the tilt with respect to the reference plane (object plane of projection optical system), phase shift, etc.), aberration of the first projection optical system (distortion, image plane curvature, astigmatism, coma aberration, spherical aberration, etc.), bending and other deformation of the mask substrate, deformation of the pattern of the working mask (deformation due to bending of the working mask along with holding, the tilt with respect to the reference plane (object plane of second projection optical system), phase shift, etc.), and aberration of the second projection optical system (distortion, image plane curvature, astigmatism, coma aberration, spherical aberration, etc.)
According to the method of exposure for producing a microdevice of this aspect of the present invention, at least one of displacement of the actual projected point (xcex21) on the mask substrate from the ideal projected point (xcex11) (first displacement) and displacement of the actual projected point (xcex21) on the device substrate from the ideal projected point (xcex11) (second displacement) is found and the pattern (36) formed on the master mask is distorted for formation based on the found displacement.
When distorting the pattern by finding the first displacement, a predetermined sampling point (xcex10) is set on the master mask, the displacement (offset) of the actual projected point (xcex21) with respect to the ideal projected point (xcex11) on the mask substrate is theoretically calculated or is found by performing actual exposure and measuring by a measuring device, the distortion of the image of the pattern on the mask substrate (4) is found based on this, and the original pattern (design pattern) to be formed on the master mask is made to distort to substantially eliminate this distortion, that is, the data of the pattern in the design is corrected to form (draw) the pattern.
When distorting the pattern by finding the second displacement or when distorting the pattern by finding both of the first and second displacements, a predetermined sampling point (xcex10) is set on the master mask or working mask, the displacement (offset) of the actual projected point (xcex21) with respect to the ideal projected point (xcex11) on the device substrate (W) corresponding to the sampling point is theoretically calculated or is found by performing actual exposure and measuring by a measuring device, the distortion of the image of the pattern on the device substrate is found based on this, and the original pattern (design pattern) to be formed on the master mask is made to distort to substantially eliminate this distortion, that is, the data of the pattern in the design is corrected to form (draw) the pattern.
The sampling point may be made a plurality of points arranged at a suitable pitch along the design pattern or in an ideal lattice. The correction values of the data at each point in the design pattern may be found based on the displacement found interpolation by the least square method or another approximation method. Since the original pattern (design pattern) to be formed on the working mask is made to distort so that the actual projected image becomes substantially in register with the ideal projected image, even if for example there is residual aberration of the projection optical system etc., it is possible to project and transfer a pattern close to the ideal image on to the device substrate and possible to produce a high accuracy, high quality microdevice. Note that instead of causing distortion of at least part of the pattern, it is also possible to cause the pattern position at the object plane side of the projection optical system to shift or to combine the two techniques.
The microdevice of the present invention produced using the above method of exposure for producing the microdevice is formed with a pattern close to the ideal image, so it is possible to improve the overlay accuracy of the pattern and obtain superior characteristics.
7. According to a seventh aspect of the present invention, there is provided a method of producing a photomask (34) on which a pattern for transfer (27) is formed, the method of producing a photomask characterized by dividing an enlarged pattern of the pattern for transfer into patterns of a plurality of master masks (R1 to RN); forming an alignment mark (24A, 24B) on a surface of a substrate (4) for the photomask; and successively transferring reduced images of the patterns of the plurality of master masks (R1 to RN) on the surface of the substrate (4) for the photomask while stitching them while aligning the substrate (4) for a photomask and the master mask (R1 to RN) using the alignment mark (24A to 24B).
According to this aspect of the present invention, since an alignment mark is formed on the substrate for the photomask and that alignment mark is used for aligning a master mask and the photomask substrate when projecting and transferring the pattern of the master mask on the photomask substrate, the pattern transferred on to the photomask substrate becomes accurately aligned with the alignment mark, there is little rotation, offset, or other error between the alignment mark and pattern as in the past, and therefore it is possible to produce a photomask with a high quality.
The photomask of the present invention produced using this method of production of a photomask has little rotation, offset, or other error between the alignment mark and the pattern formed on its surface as in the past and therefore is high in accuracy and high in quality.
When transferring and exposing a pattern on a device substrate using such a high accuracy, high quality photomask, the alignment mark (24A, 24B) of the photomask (34) is used to align the photomask and the device substrate (W). The alignment mark formed on the photomask is used for alignment when transferring the pattern of the master mask on the photomask substrate for producing the photomask. An alignment mark the same as the alignment mark at this time is used for the alignment when transferring the pattern to the device substrate. Therefore, there is little room for error to enter compared with when forming alignment marks independently, it is possible to improve the positional accuracy of the pattern formed on the device substrate, and in turn it is possible to produce a microdevice with good characteristics.
Note that in this case, when successively transferring reduced images of the plurality of master masks (R1 to RN) on the surface of the substrate (4), it is preferable to selectively use a block exposure type reduction projection exposure apparatus or a scan exposure type reduction projection exposure apparatus according to the application of the photomask (type of exposure apparatus used etc.) For example, when the photomask is to be used in a scan exposure type reduction projection exposure apparatus such as a step-and-scan type, parallelogram shaped distortion (so-called xe2x80x9cskew errorxe2x80x9d) etc. sometimes occurs in the projected image. In this case, since skew error is difficult to correct with the block exposure system, by using a scan exposure type projection exposure apparatus when transferring the patterns of a plurality of master masks on the photomask substrate, it is possible to reduce the distortion when using the photomask, therefore the overlay error etc. becomes smaller.
Further, when successively transferring the reduced images of the patterns of the plurality of master masks (R1 to RN) on the surface of the substrate (4), it is desirable to correct the imaging characteristics (transfer position, magnification, distortion, etc.) of the reduced images of the patterns of the master masks (R1 to RN) in accordance with at least one of the nonrotational symmetrical aberration and distortion characteristics of the projection optical system (42) of the projection exposure apparatus using the photomask.
When the amount of variation of a predetermined imaging characteristic of the exposure apparatus using this photomask is known in advance, when transferring patterns of the master masks on the photomask substrate while stitching them, it is possible to adjust the transfer position, magnification, and distortion etc. of the pattern images of the master masks so as to cancel out the variation in the imaging characteristic and thereby reduce the distortion of the device pattern exposed using the photomask and improve the overlay accuracy etc.
In this regard, sometimes a plurality of these photomasks are produced and these photomasks used by a plurality of projection exposure apparatuses by mix-and-match etc. In this case, it is desirable to adjust the transfer position or imaging characteristics etc. at the time of transfer of the patterns of the master masks while stitching them in accordance with the average characteristics of the distortion characteristics etc. of the projected images of at least two projection exposure apparatuses scheduled to use these photomasks so as to obtain good overlap accuracy at these projection exposure apparatuses.
Next, it is preferable that the photomask be used in reduction projection. If deeming the photomask to be one used in 1/xcex2-fold (xcex2 is an integer, fraction, etc. more than 1) reduction projection, if the reduction magnification of the exposure apparatus for producing the photomask is 1/xcex1 (xcex1 is an integer, fraction, etc. larger than 1 in the same way as xcex2), the drawing error of the patterns of the master masks is reduced to 1/(xcex1xc2x7xcex2) in the device pattern finally exposed. Therefore, even if making the minimum line width of the device pattern xc2xd the current level, it would be possible to easily draw the patterns of the master masks easily and in a short time with the necessary accuracy using an electron beam lithography system or laser beam lithography system. Therefore, even if the pattern rule becomes further finer, the desired device pattern can be exposed by the necessary accuracy.
8. According to an eighth aspect of the present invention, there is provided an exposure apparatus for production of a photomask having a mask magazine (16 to 18) which stores a plurality of master masks (R1 to RN); a mask stage (2) which carries one master mask selected from the mask magazine; a projection optical system (3) which projects a reduced image of the pattern of the master mask carried on the mask stage on to a photomask substrate (4) formed with an alignment mark (24A, 24B); a substrate stage (6) which positions the photomask substrate on a plane vertical to an optical axis of the projection optical system; and an alignment system (14A, 14B) which aligns the master mask on the mask stage and the photomask substrate on the substrate stage using the alignment mark of the photomask substrate on the substrate stage so as to stitch the reduced images of the patterns of the plurality of master masks on the photomask substrate.
The method of production of a photomask according to the seventh aspect of the present invention may be worked by use of this exposure apparatus for production of a photomask. When an alignment mark is formed on the photomask substrate and transferring the pattern of the master mask on the photomask substrate, if aligning the master mask and photomask substrate by an alignment system using this alignment mark, the pattern transferred on to the photomask substrate becomes accurately aligned with the alignment mark, there is little rotation, offset, and other error between the alignment mark and pattern as in the past, and therefore a high quality photomask can be produced.
In this case, the mask magazine, as one example, stores a plurality of master masks (R1 to RN) formed with patterns obtained by dividing an enlarged pattern of the pattern (27) of the photomask to be produced. This enables the master masks to be quickly exchangeed and exposure to be performed in a short time.
9. According to a ninth aspect of the present invention, there is provided an exposure apparatus for producing a device projecting an image of a pattern on a photomask (34) according to the present invention on to a device substrate (W), the exposure apparatus characterized by having a mask stage which carries the photomask; a projection optical system (42) which projects a reduced image of a pattern of the photomask carried on the mask stage on to the device substrate; a substrate stage (44) which positions the device substrate on a plane vertical to an optical axis (AX1) of the projection optical system; and an alignment system (41A, 41B) which aligns the photomask on the mask stage and the device substrate on the substrate stage using the alignment mark (24A, 24B) of the photomask on the mask stage so as to project the pattern (27) of the photomask on the the device substrate.
The above-mentioned methods of exposure of the present invention can be worked by using this exposure apparatus for production of a device. The alignment mark formed on the photomask is used for alignment when forming the pattern of the master mask on the photomask substrate for producing the photomask. An alignment mark the same as the alignment mark at this time is used for the alignment when forming the pattern to the device substrate. Therefore, there is little room for error to enter compared with when forming alignment marks independently, it is possible to improve the positional accuracy of the pattern formed on the device substrate, and in turn it is possible to produce a microdevice with good characteristics.
Further, according to the present invention, if the magnification from the pattern of the device formed on the device substrate (W) to the pattern (27) of the photomask is xcex2 (xcex2 is an integer, fraction, etc. more than 1) and the magnification from the pattern of the photomask to the pattern (36) of the master mask is xcex1 (xcex1 is an integer, fraction, etc. larger than 1 in the same way as xcex2), the line width of the pattern of the master mask becomes xcex1xc2x7xcex2 the line width of the pattern of the device. Therefore, if the drawing error of the line width when drawing the pattern of the master mask by an electron beam lithography system is xcex94d, the error of the line width of the pattern of the device is reduced to about xcex94d/(xcex1xc2x7xcex2), so the pattern of the device can be formed with an extremely high accuracy.
10. According to a 10th aspect of the present invention, there is provided a method of production of a microdevice characterized by forming an alignment mark (24A, 24B) on a first substrate (4) for a photomask, dividing a device pattern to be transferred on to a second substrate (W) on which the microdevice is to be formed into a plurality of element patterns, transferring reduced images of the plurality of element patterns on to the first substrate to form a device pattern using positional information obtained by detecting the alignment mark, and transferring the device pattern on to the second substrate using the alignment mark of the photomask on which the device pattern is formed.
According to this method of production of a microdevice, the alignment mark formed on the photomask is used for alignment when transferring the element pattern on the first substrate for producing the photomask. An alignment mark the same as the alignment mark at this time is used for the alignment when forming the pattern on the second substrate and then the pattern transferred, so there is little room for error to enter compared with when forming alignment marks independently, it is possible to improve the positional accuracy of the pattern formed on the second substrate, and in turn it is possible to produce a microdevice with good characteristics.
11. According to an 11th aspect of the present invention, there is provided a method of exposure using a plurality of masks to transfer patterns on a photosensitive substrate in a plurality of partially overlapping areas, the method of exposure characterized by making the amount of exposure at part of the plurality of areas at the time of transfer of the pattern different from the amount of exposure at other areas.
Further, using this method of exposure, a method of production of a photomask including the step of transferring a plurality of patterns on the photomask substrate by a step-and-stitch can be provided.
Further, using this method of exposure, a method of production of a device including the step of transferring a plurality of patterns on the photomask substrate by a step-and-stitch can be provided.
12. According to a 12th aspect of the present invention, there is provided a method of exposure emitting an illumination beam to a mask and exposing a photosensitive substrate by the illumination beam through a projection optical system, the method of exposure characterized by detecting an image projected by the projection optical system at a plurality of different points in an area illuminated by the illumination beam to obtain first information, adjusting optical characteristics of the projected image based on the same, detecting an image projected by the projection optical system at least at one measurement point outside of the illuminated area in a state with the optical characteristics adjusted to obtain second information, and storing the same and adjusting characteristics of the pattern image by the projection optical system using the second information so as to expose the photosensitive substrate by the illumination beam using the mask. In this case, it is possible to detect a mark positioned outside of the illuminated area on the mask and adjust the characteristics of the pattern image based on the second information and third information obtained by detection of that mark. The mark is for example formed at a plurality of different positions outside the pattern area on the mask on which the pattern to be transferred to the photosensitive substrate is formed.
The first and second information can be obtained using a specific mask different from the above mask. In this case, it is possible to use a specific mask having a first area corresponding to the pattern area and having a second area outside of the same in which the plurality of marks are formed, obtaining the first information by detection of a mark in the first area, and obtaining the second information by detection of a mark in the second area.
Using the above method of exposure, a method of production of a device including the step of transferring a device pattern to a workpiece can be provided.
Further, using the above method of exposure, a method of production of a photomask including the step of transferring patterns formed on a plurality of master masks on to a photomask substrate by the step-and-stitch system can be provided. In this case, it is possible to reducing and projecting the patterns of the master masks through the projection optical system, enlarge a device pattern to be formed on the photomask by exactly an inverse magnification of a projection magnification of the projection optical system, divide the enlarged pattern into elements or functions, and form the same on the plurality of master masks.
13. According to a 13th aspect of the present invention, there is provided a method of production of a photomask for use in an exposure apparatus, the method of production of a photomask characterized by exposing a plurality of partially overlapping areas on a substrate for the photomask using a plurality of master masks formed by dividing an enlarged pattern of a device pattern to be formed on the photomask into a plurality of sections and by adjusting at least one of a shape and position of a reduced image of a divided pattern on the substrate based on transfer characteristics of the master masks by the exposure apparatus. In this case, it is possible to modify design data of a divided pattern produced from the enlarged pattern and form the divided pattern on a master mask in accordance with the modified design data. Further, it is possible to adjust optical characteristics of a projection optical system forming a reduced image of a divided pattern based on the transfer characteristics. Further, it is possible to transfer a divided pattern on the substrate by synchronously moving the master mask and the substrate for scan exposure of the plurality of areas and adjust the shape of the reduced image by changing conditions of the scan exposure based on the transfer characteristics.